build

🔩🛠️ brief notes on the build, optimised for junk/materials on hand..

The metal frame base was up-cycled from a junk treadmill and paired with galvanised (M8) threaded rod using M8 nuts and washers. Modified Zevro KCH-06139 wall mounted cereal dispenser was used as main payload delivery, secured to offset slotted steel angle with three eight millimetre pop rivets. See images for how the servos are coupled to the dispenser knobs. The rest of the delivery was hacked together from 45 degree elbows and central vacuum PVC pipe, cut at 45 degree angle at the end touching the bowls and attached to the vertical rods with some more threaded rod and clamps. Servos are held in place with left over car roof awning brackets, secured onto vertical shafts (threaded rod) with nuts and washers and padded with some packaging foam.

The center dispenser was modified to hold water by gluing the bottom plug shut with pour resin and adding a 1/4" push-fit tube bulkhead (drill in the bulkhead first, before pouring). Water is then gravity fed via 12VDC 1/4" push-fit solenoid valve and water level sensor relay board. The water sensor is a length of 1/4" HVAC copper pipe flared on one end, covered with corrugated electrical conduit with three copper wire rings for connection to the relay board and a 1/4" compression coupling to solenoid valve.

All electronics, buttons and switches fit in between the slotted angles. Aside from RPi Zero W and case left over from another project, I used a common step-down buck converter to bring 12VDC down to 5VDC for the RPi. Everything was soldered onto a breadboard, which was installed in old hair product plastic box with holes drilled in for cabling. The camera is an old RPi module (~ v1.3) with a fish eye lens replacing the stock lens. It's housed in an old dental floss box and secured under the slotted steel angle with velcro tape.

The main ifeed software is written in Python and held together with Bash scrips in a "balenafied" Docker compose. Servos can be controlled by momentary switches as well as Linux SIGUSR signals. I used USR1 for snack and USR2 for meal. The only difference between the two is the amount of time the servos run, defined in config.py. The iwait scheduler execs into the ifeed container on a cron schedule and dispenses by sending an appropriate signal to the Python process.

My istream solution can stream to an RTMP sink as well as take timelapse stills. Streaming on RPi Zero is marginal and doesn't leave enough compute to run the servos properly. I left it there as an option to use on higher powered devices, but for RPi Zero(s), I set ISTREAM_STILL environment variable instead.

The composition is deployed to balenaCloud for convenience. Because RPi Zero is weak, I used a tiny nweb HTTP server, as well as netcat to serve images/pages and Traefik for reverse proxying it. I also used Fastly to cache everything for 60s and provide TLS.